Abrasive articles enjoy utility in a variety of industrial applications for abrading, finishing and polishing a variety of surfaces. Typical industrial uses of abrasive articles include polishing a substrate, as during various phases in manufacturing semiconductor devices and magnetic recording media. In manufacturing semiconductor devices, a wafer typically undergoes numerous processing steps, including deposition, patterning and etching. After various processing steps it is necessary to achieve a high level of surface planarity and uniformity to enable accurate photolithographic processing. A conventional planarization technique comprises polishing, as by CMP, wherein a wafer carrier assembly is rotated in contact with a polishing pad in a CMP apparatus. The polishing pad is mounted on a rotating/moving turntable or platen driven by an external driving force. The wafers are typically mounted on a carrier or polishing head which provides a controllable force, i.e., pressure, pressing the wafers against the rotating polishing pad. Thus, the CMP apparatus effects polishing or rubbing movement between the surface of each thin semiconductor wafer and the polishing pad while dispersing a polishing slurry containing abrasive particles in a reactive solution to effect both chemical activity and mechanical activity while applying a force between the wafer and a polishing pad.
Conventional polishing pads employed in abrasive slurry processing typically comprise a grooved porous polymeric surface, such as polyurethane, and the abrasive slurry varied in accordance with the particular material undergoing CMP. Basically, the abrasive slurry is impregnated into the pores of the polymeric surface while the grooves convey the abrasive slurry to the wafer undergoing CMP. A polishing pad for use in CMP slurry processing is disclosed by Krywanczyk et al. in U.S. Pat. No. 5,842,910. Typical CMP is performed not only on a silicon wafer itself, but on various dielectric layers, such as silicon oxide, conductive layers, such as aluminum and copper, or a layer containing both conductive and dielectric materials as in damascene processing.
A distinctly different type of abrasive article from the above-mentioned abrasive slurry-type polishing pad is a fixed abrasive article, e.g., fixed abrasive polishing sheet or pad. Such a fixed abrasive article typically comprises a backing with a plurality of geometric abrasive composite elements adhered thereto. The abrasive elements typically comprise a plurality of abrasive particles in a binder, e.g., a polymeric binder. During CMP employing a fixed abrasive article, the substrate or wafer undergoing CMP wears away the fixed abrasive elements thereby releasing the abrasive particles. Accordingly, during CMP employing a fixed abrasive article, a chemical agent is dispersed to provide the chemical activity, while the mechanical activity is provided by the fixed abrasive elements and abrasive particles released therefrom by abrasion with the substrate undergoing CMP. Thus, such fixed abrasive articles do not require the use of a slurry containing loose abrasive particles and advantageously simplify effluent treatment, reduce the cost of consumables and reduce dishing as compared to polishing pads that require an abrasive slurry. During CMP employing a fixed abrasive polishing pad, a chemical agent is applied to the pad, the agent depending upon the particular material or materials undergoing CMP. However, the chemical agent does not contain abrasive particles as in abrasive slurry-type CMP operations. Fixed abrasive articles are disclosed by Rutherford et al. in U.S. Pat. No. 5,692,950, Calhoun in U.S. Pat. No. 5,820,450, Haas et al. in U.S. Pat. No. 5,453,312 and Hibbard et al. in U.S. Pat. No. 5,454,844.
Fixed abrasive elements are typically formed by filling recesses in an embossed carrier with a slurry comprising a plurality of abrasive grains dispersed in a hardening binder precursor and hardening the binder precursor to form individual abrasive composite elements that are laminated to a backing sheet and the embossed carrier removed. The backing sheet containing the individual abrasive composite elements adhered thereto is then typically mounted to a subpad containing a resilient element and a rigid element between the backing sheet and the resilient element. Such mounting can be effected by any of various types of laminating techniques, including the use of an adhesive layer. Methods of forming a backing sheet containing fixed abrasive elements are disclosed by Calhoun in U.S. Pat. No. 5,437,754 as well as Rutherford et al. in U.S. Pat. No. 5,692,950.
Fixed abrasive elements of conventional slurry-less type polishing pads are typically formed in various "positive" geometric configurations, such as a cylindrical, cubical, truncated cylindrical, and truncated pyramidal shapes, as disclosed by Calhoun in U.S. Pat. 5,820,450. Conventional fixed abrasive articles also comprise "negative" abrasive elements, such as disclosed by Ravipati et al. in U.S. Pat. No. 5,014,468.
During CMP, the surface of conventional polymeric polishing pads for abrasive-slurry type CMP operations becomes glazed thus nonreceptive to accommodating and/or dispensing the abrasive slurry and is otherwise incapable of polishing at a satisfactory rate and uniformity. Accordingly, conventional practices comprise periodically conditioning the pad surface so that it is maintained in a proper form for CMP. Conventional conditioning means comprises a diamond or silicon carbide (SiC) conditioning disk to conditioning the polishing pad. After repeated conditioning operations, the pad is eventually consumed and incapable of polishing at a satisfactory rate and uniformity. At this point, the polishing pad must be replaced. During replacement, the CMP apparatus is unavailable for polishing with an attendant significant decrease in production throughput.
On the other hand, fixed abrasive pads do not undergo the same type of adverse smoothing as do conventional polymeric pads. Moreover, a fixed abrasive pad has a low contact ratio (area of the tops of abrasive elements/total pad area), e.g., about 10% to about 25% and short abrasive elements. Periodic pad conditioning with conventional conditioning means would drastically reduce the pad lifetime on a CMP apparatus having a rotating round platen. Preconditioning only would be expected to adversely affect the polishing rate and uniformity stability, i.e., wafer-to-wafer uniformity, since preconditioning with conventional diamond or SiC disks would be expected to render the pad surface significantly different from that caused by pad-wafer interactions. Accordingly, conventional practices on fixed abrasive pads do not involve preconditioning, i.e., prior to initial CMP, or periodic conditioning, after initial CMP. However, the use of fixed abrasive articles, such as polishing pads, disadvantageously results in poor wafer-to-wafer polishing rate stability on a CMP polisher having a rotating round platen or on a polisher with an advanceable polishing sheet at an indexing rate less than 0.5 to 1.0 inch per minute.
Copending U.S. application Ser. No. 09/244,456 filed Feb. 4, 1999 and assigned to the assignee of the present invention discloses a CMP apparatus having a rotatable platen, a polishing station with a generally linear polishing sheet having an exposed portion extending over a top surface of the platen for polishing the substrate, and a drive mechanism to incrementally advance the polishing sheet in a linear direction across a top surface of the platen. The polishing sheet is releasably secured to the platen to rotate with the platen, and it has a width greater than the diameter of the substrate. Thus, an unused portion of the polishing sheet is incrementally advanced or indexed after polishing a wafer, e.g., by exposing about 0.5 inch to about 1 inch per minute of virgin or unused polishing pad surface. In this way, wafer-to-wafer rate stability is improved. The entire disclosure of U.S. application Ser. No. 09/244,456 is hereby incorporated by reference herein. However, indexing of 0.5 to 1 inch per minute of pad significantly reduces the useful life of fixed abrasive polishing sheets, condemning them to the trash bin before the abrasive elements are consumed to any significant extent, thereby significantly increasing manufacturing costs.
There exists a need to extend the useful life of a fixed abrasive article, e.g., polishing sheet or pad, while simultaneously maintaining high wafer-to-wafer rate stability. There also exists a need for a CMP apparatus enabling the use of fixed abrasive polishing pads having an extended life and achieving high wafer-to-wafer rate stability.